Solution:
First insure that you have the PHP Apache module installed.
ls -l /etc/httpd/conf.d/php.conf
If you don’t have that file then you may just have the php-cli (command line interface) installed without the php Apache httpd module. To install run the command:
sudo yum install php -y
Then restart your httpd server:
sudo service httpd restart
For Apache httpd to process index.php files, you need to update your DirectoryIndex to handle PHP directory indexes.
On Centos edit the file:
/etc/httpd/conf/httpd.conf
Search for the line starting:
DirectoryIndex
And add the following to the space delimited list of index filenames:
index.php
Directory index files will be recognized in the order they are defined.
You will also need to restart your httpd service using:
sudo service httpd reload
Alternatively you can use the apachectl utility to reload httpd gracefully
sudo apachectl graceful